1913-] STEVENSON— FORMATION OF COAL BEDS. 141 



there is no other conceivable set of conditions whereby the supposed 

 cover of vegetation could be removed. The mass of more or less 

 disintegrated and decomposed plant materials on the surface was 

 very thick ; rain falling on this would be absorbed and the material 

 would be cemented. The roots of plants would resist movement of 

 the water; those roots form a network which, under very unfavor- 

 able circumstances, suffices to check that movement; a handful of 

 loose sandy clay on a sloping shelf in a railway cut is hardly dimin- 

 ished by a dashing shower or the accompanying rills, if only a bunch 

 of grass have thrust its roots through it. How much greater would 

 be the resistance of the dense vegetation, one can hardly conceive. 

 It would be impossible for a flood to retain any force after encoun- 

 tering such a wall, even though the slope were somewhat steep and 

 though the water had been ploughing the surface for some distance. 

 The observations recorded by Marsh^^' make this sufficiently clear. 

 Any one who has stood at the edge of a wooded river-bottom during 

 time of high flood, knows that, no matter how the water rages out- 

 side, quiet reigns within that area and the overflow moves gently. 

 Where vegetation is dense, no flood does damage. A flood can never 

 gain speed in a rolling country covered with such vegetation as sup- 

 posed by Renault and others ; within the matt of plants it would be 

 as powerless for injury as is a great mass of snow on a densely 

 wooded slope. One cannot repeat too often or emphasize too 

 strongly that running water does not strip off a vegetable cover, that 

 floods do not uproot forests, do not tear away beds of peat. This has 

 been shown in Part II. of this work. Be it understood there is no 

 reference here to digging of a new channel-ways by debris-iaden 

 streams; or to such local accidents as disturbances of the vegetable 

 cover by eddies around stumps or large bowlders in an open area ; or 

 even to bursting bogs. Such accidents aft'ecting a few rods or even 

 acres, are very important to the farmer whose pet meadow has been 

 ruined, but they are without interest to one studying conditions 

 within areas of many square miles or along flood lines, scores to 

 hundreds of miles long. 



Allochthony applies one set of phenomena, occurring under defi- 



"'." Formation of Coal Beds," II., these Proceedings, Vol. L., p. 531. 



